My 03 crew cab short box 2wd Duramax ZF 6-speed truck has a shudder when I get on the gas. I'm pulling a 9000# trailer and was running a box in the over 100 hp range. (It's a test mule box and doesn't have different settings) When the box is disconnected there's no problem. With the box connected and no trailer there's no problem. Two questions: First is it the dual mass flywheel bottoming its springs or is it the driveline? I'm inclined to think its drive line. Some clutch guys have told me a dual mass does bottom when ever you trounce the gas. Second, Is my ZF truck covered under the one piece drive shaft TSB?